In recent years, the electronic equipment market has earnestly demanded downsizing and functional improvement of various electronic equipment with built-in component-mounted boards formed by placing and mounting a plurality of electronic components onto a circuit board. Therefore, it is required to perform high-density mounting (or placement) and high-accuracy mounting (or placement) of electronic components in forming a component-mounted board. It is further demanded to reduce a production cost of component-mounted boards. For example, it is additionally demanded to improve productivity per unit area of component-mounted boards, i.e., productivity per unit area in mounting electronic components.
Such a component-mounted board is manufactured by placing a plurality of electronic components onto a circuit board, and thereafter heating the circuit board on which the electronic components are placed in a reflow manner for mounting of the electronic components placed on the circuit board. Such a manufacturing process is called a component mounting process (or component-mounted board production process), which is categorized roughly into a component placement process and a reflow process. The component placement process is performed by an electronic component placement apparatus provided with a component placement head that sucks and holds a plurality of electronic components and places them onto a circuit board.
FIG. 4 shows a sectional view of a head section 500 that is one example of a component placement head employed in such a conventional electronic component placement apparatus (refer to, for example, Japanese unexamined Patent Publication No. 2000-40900), and structure of the head section 500 will be described with reference to FIG. 4.
As shown in FIG. 4, the head section 500 is provided with a suction nozzle 502 that is one example of a component holding member for releasably holding an electronic component 501 such as a chip component, a shaft section 510 that is one example of a shaft section detachably equipped with this suction nozzle 502, an elevation unit 520 for moving up and down the suction nozzle 502 equipped for the shaft section 510 via this shaft section 510, and a rotating unit 530 for rotating the suction nozzle 502 around its axis of rotation (its axial center of rotation) via the shaft section 510.
Moreover, in order to improve efficiency of an operation of placing electronic components 501 onto a circuit board by providing the head section 500 with a plurality of suction nozzles 502 capable of individually sucking and holding electronic components 501, the head section 500 is provided with, for example, eight sets of shaft sections 510 and elevation units 520, and the shaft sections 510 and the elevation units 520 are supported by a head frame 540 of the head section 500 so that the shaft sections 510 are arranged in a line (i.e., the suction nozzles 502 are arranged in a line). Moreover, the rotating unit 530 is able to rotate four suction nozzles 502 equipped for four mutually adjacent shaft sections 510. In the head section 500 capable of being equipped with eight suction nozzles 502, two rotating units 530 are provided while being supported by the head frame 540, by which the suction nozzles 502 equipped for the shaft sections 510 are made rotatable.
With regard to the head section 500 having the above-mentioned construction, a detailed structure of the shaft section 510 will be described first. As shown in FIG. 4, each shaft section 510 is provided with a spline shaft 511 that has a nozzle attaching portion 511a, which is one example of a holding member attaching portion capable of being detachably equipped with the suction nozzle 502, at its end portion (lower end in this figure). Moreover, the spline shaft 511 is able to rotate around its axis of rotation P by the rotating unit 530 corresponding to this shaft section 510, and elevatable along axis of rotation P by a corresponding elevation unit 520. In the shaft sections 510, spline shafts 511 are elevatable and rotatable as described above while being supported as the shaft sections 510 by the head frame 540. This support structure will be described by using a partially enlarged schematic view of the shaft section 510 shown in FIG. 5.
As shown in FIG. 5, the shaft section 510 is further provided with a first spline nut 512 (arranged on an upper side in this figure) and a second spline nut 513 (arranged on a lower side in the figure), which are arranged apart from each other along axis of rotation P of the spline shaft 511, and which are two spline nuts that elevatably support the spline shaft 511.
Moreover, as shown in FIG. 5, the first spline nut 512 and the second spline nut 513 are supported via a bearing section 514 and a bearing section 515, respectively, to a shaft frame 541 rotatably around axis of rotation P together with the spline shaft 511 on an inner periphery of the shaft frame 541, that has a roughly cylindrical shape, in the head frame 540. Moreover, a roughly cylindrical outer cylinder collar 516 has its inner peripheral surface bonded to an outer periphery of the first spline nut 512, and an outer periphery of the outer cylindrical collar 516 is further rotatably supported on an inner periphery of the shaft frame 541 via another bearing section 517, rotatably supporting the first spline nut 512. Moreover, an outer cylindrical collar 518 is similarly bonded to the second spline nut 513 and rotatably supported via another bearing section 519.
With the shaft section 510 having the above-mentioned structure, the spline shaft 511 is elevatable along axis of rotation P on the inner periphery of the first spline nut 512 and the second spline nut 513 in the shaft section 510, and both the first spline nut 512 and the second spline nut 513 are made rotatable around axis of rotation P on the inner periphery of the shaft frame 541.
Detailed structure of the rotating unit 530 will be described next. As shown in FIG. 4, the rotating unit 530 is provided with a shaft gear 531 arranged so that the spline shaft 511 penetrates a cylindrical inner portion thereof. Moreover, the shaft gear 531 rotates the first spline nut 512 by rotation around axis of rotation P thereof, thereby allowing the spline shaft 511 to be rotated. Further, the rotating unit 530 is provided with a cogged belt 532 engaged with the shaft gear 531, a driving gear 533 engaged with the cogged belt 532, and a rotating drive motor 534 at an end of its driving shaft 534a to which the driving gear 533 is fixed and which is able to rotate the driving shaft 534a in either a forward or reverse direction.
Moreover, as shown in FIG. 5, the shaft gear 531 has its lower end connected to an upper end portion 516a, in this figure, of an outer cylindrical collar 516 bonded to the first spline nut 512 via a ring-shaped coupling 535. Moreover, the shaft gear 531 is supported on an inner peripheral surface of the shaft frame 541 so as to be rotatable around axis of rotation P via two bearing sections 536 at an upper end and a lower end of its outer peripheral surface, and so as not to come into contact with the spline shaft 511. Moreover, a plurality of teeth are continuously provided on an outer peripheral surface of the shaft gear 531, an inner peripheral surface of the cogged belt 532 and an outer peripheral surface of the driving gear 533, in order to strengthen mutual engagement.
In this case, relations of planes among the shaft gear 531, the cogged belt 532 and the driving gear 533 will be described here with reference to a schematic explanatory view shown in FIG. 6. As shown in FIG. 6, one driving gear 533 and four mutually adjacent shaft gears 531 are engaged with one another inside one cogged belt 532. That is, by rotatively driving the driving gear 533 in either the forward or reverse direction by the rotating drive motor 534, the cogged belt 532 is driven to run in a rotational drive direction, thereby allowing the four shaft gears 531 to be concurrently rotated in the rotational drive direction. Moreover, between the shaft gears 531 and between the shaft gear 531 located at the left-hand end in this figure and the driving gear 533, four tension rollers 537 are provided so as to consistently inwardly urge the cogged belt 532, thereby consistently applying a constant tension to the cogged belt 532 and maintaining a satisfactory engagement relationship among the gears.
With the rotating unit 530 having the above-mentioned structure, the spline shafts 511 corresponding to the four shaft gears 531 can be rotated around axis of rotation P concurrently in the same rotational direction via the coupling 535 and the first spline nut 512.
The elevation unit 520 will be described next. As shown in FIG. 4, the elevation unit 520 is provided with a ball screw shaft 521 supported, by an elevation frame 542 of the head frame 540, rotatably around axis of rotation Q (an axial center of rotation) thereof arranged roughly parallel to axis of rotation P of the spline shaft 511. The elevation unit 520 is further provided with an elevation drive motor 522, which is fixed to an upper end portion, in this figure, of the ball screw shaft 521 and rotates the ball screw shaft 521 in either a forward or reverse direction around axis of rotation Q, and an elevation nut section 523, which is meshed with the ball screw shaft 521 and is moved up and down along axis of rotation Q by rotation of the ball screw shaft 521. Moreover, the elevation unit 520 is further provided with a roughly L-figured elevation bar 524, which has one end fixed to the elevation nut section 523 and is moved up and down in accordance with ascent and descent of the elevation nut section 523, and another end of the elevation bar 524 is arranged so as to be placed between two bearing sections 525 attached to an upper portion of the spline shaft 511.
With the above-mentioned structure possessed by the elevation unit 520, when the elevation nut section 523 is moved up or down by rotation of the ball screw shaft 521, the elevation bar 524 is moved up or down to push up or push down the spline shaft 511 via the bearing sections 525 by its end portion, thereby allowing the spline shaft 511 to be moved up and down. It is to be noted that ascent and descent of the elevation bar 524 is guided by an LM guide 526 provided on the elevation frame 542.
Moreover, as a component placement head as described above, there has conventionally been a head section provided with a plurality of suction nozzles that serve as one example of component holding members arranged in a line. In the head section described above, efficiency of placing components onto a circuit board has been improved by making the suction nozzles concurrently suck and hold a plurality of components. Moreover, during such a component placement operation by the head section, an elevating operation of the suction nozzles is to be performed. However, due to a necessity for performing individual elevating operations of the suction nozzles, the head section is provided with elevation units corresponding one to one to the suction nozzles.
Moreover, the head section described above is generally able to individually perform the elevating operation of the suction nozzles by generally performing an elevating operation of the shaft sections capable of being detachably equipped with a suction nozzle at its end by respective elevation units (these shaft sections are also provided for the head section while being arranged in a line). Moreover, the elevation units generally employ a mechanism employing a ball screw shaft section and a nut section meshed therewith, and rotatively drive the ball screw shaft section by rotatively driving the drive motor attached to the ball screw shaft section, thereby moving up and down the nut section and enabling the elevating operation of the shaft section in a state in which it can be moved up and down in synchronization with ascent and descent of the nut section while being engaged with the nut section.
Next, FIG. 14 shows a schematic explanatory view of elevation units 410 of the head section 400 described above, and a method for detecting an origin that becomes a reference point of ascent and descent of each of the elevation units 410 (refer to, for example, Japanese unexamined Patent Publication No. 62-236655) will be described with reference to FIG. 14.
As shown in FIG. 14, the head section 400 is provided with eight elevation units 410, i.e., eight suction nozzles (not shown). Moreover, each of the elevation units 410 is provided with a ball screw shaft section 411, a nut section 412, a drive motor 413 and an upper end position restricting frame 414 for restricting an upper end position of elevation of the nut section 412.
Moreover, the head section 400 is provided with a control section 409 capable of individually controlling these elevation units 410. Each of the elevation units 410 is further provided with an encoder (not shown) capable of detecting a rotational angle of the drive motor 413 and outputting this detection result to the control section 409.
When detecting an origin in the head section 400 described above, by detecting the rotational angle by the encoder while rotatively driving the drive motor 413 in each of the elevation units 410 and assuming a position of the nut section 412 on an elevating operational axis when the origin of rotation in the rotational direction is detected as the origin (hereinafter referred to as a detection origin), each of plural detection origins is set by the control section 409.
It is to be noted that these operations may be executed either individually or concurrently in the elevation units 410. Subsequently, an elevating operation of each of the suction nozzles for a component placement operation is executed in the head section 400 regarding a detection origin thus set as an origin on an actual elevating operational axis (hereinafter referred to as an axial origin).